Control Device For A Compressor, A Compressor With The Same, And An Air Conditioning System Including Control Device And Compressor

ABSTRACT

A compressor control module (CCM) controls an output of a variable displacement swash plate compressor. The CCM directly calculates, or receives from an external source, a signal indicating a desired or required output from the compressor, receives a current value of the desired or required output, and receives or calculates a current rotation speed and angle, with respect to a rotation axis, of a swash plate, or a current piston stroke length and a reciprocating frequency of the compressor. The CCM determines a difference between the desired or required output from the compressor and the current value and outputs a signal to a valve driving unit which will adjust an angle of a swash plate such that the actual value becomes closer to, or the same as, the desired or required output, taking into account the additional values received or calculated in the receives or calculates step.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of the filing date under 35 U.S.C. § 119(a)-(d) of European Patent Application No. 19170851.0, filed on Apr. 24, 2019.

FIELD OF THE INVENTION

The present invention relates to a compressor control module and, more particularly, to a compressor control module for controlling the operation of a variable displacement swash plate compressor.

BACKGROUND

In general, air-conditioning systems for vehicles are equipped with a refrigerant compression cycle system for cooling and/or heating. The heart of the refrigerant compression cycle is a compressor that compresses and circulates refrigerant in the refrigerant cycle. The compressor is typically configured to keep the pressure in the evaporator at a low level. The pressure in the evaporator directly relates to the temperature of saturated refrigerant throttled into the evaporator, and hence, by keeping the pressure low, the compressor keeps the temperature low in the evaporator.

The variable displacement swash plate type compressor is popular for vehicle air-condition systems. The variable displacement swash plate compressor is typically driven by a belt driven by the vehicle engine. The compressor output (such as compressor load or compressor work done on fluid) can be adjusted by shifting an angle of a swash plate.

The variable displacement swash plate compressor is configured so that a rotating swash plate's inclination angle affects the reciprocation length of compression pistons. The inclination angle of the swash plate, in turn, is typically regulated by varying a pressure difference between a crank chamber of the variable displacement swash plate compressor and suction chamber thereof. That is, when the pressure in the crank chamber is increased by directing high-pressure working fluid from the discharge chamber to the crank chamber, the pressure difference between the crank chamber and the suction chamber (Pc−Ps) increases, and the swash plate angle decreases (i.e. is moved perpendicular to a main shaft), so the stroke of the piston is reduced. Accordingly, when the pressure in the crank chamber is decreased, the swash plate angle is increased and the stroke of the piston is increased, leading to increased compressor mass flow rate.

The crank chamber of the variable displacement swash plate compressors in the prior art is in constant communication with the suction chamber via a fixed orifice, often termed “bleed port”. With a control valve closing the passage between the crank chamber and the discharge chamber, the pressure in the crank chamber, due to the bleed port, decreases until it reaches the pressure in the suction chamber. This will increase the inclination angle of the swash plate to maximum, and consequently, the strokes of the pistons, increasing the compressor mass flow.

The prior art control of swash plate angle is done by regulating the flow of the high-pressure working fluid from the discharge chamber to the crank chamber. Mainly the pressure difference between the resulting crank case pressure and suction pressure (Pc−Ps) defines the swash plate angle. This configuration of the prior art is well known and simple but has disadvantages. The bleed port between suction chamber and the crank chamber leads to pressure losses that could otherwise be used for cooling. Another disadvantage is that the prior art control tends to be unstable in certain conditions.

The electronic control valve used by a so-called “externally controlled variable compressor” typically includes an actuating rod driven by an electronic actuator such as a solenoid. The actuating rod moves valve bodies, depending upon the turning on/off of the solenoid. The externally controlled variable compressor can adjust the temperature at the outlet of an evaporator, for example, within a range of up to 12° C. By adjusting the temperature in the evaporator, the AC system can be optimized for cooling load, leading to more efficient cooling, and reduced power consumption.

Further, since the electrical control valve in some embodiments may control the swash plate to be perpendicular to the main shaft, setting the compressor output/load to a minimum, the mechanism for otherwise turning the compressor on/off (usually a clutch) can be dispensed with, simplifying the construction and reducing manufacturing costs.

The prior art typically involves an open-loop regulation of the suction pressure. A Heating Ventilation and Air Conditioning (HVAC) system sets a desired suction pressure for the compressor. The desired suction pressure is translated into a certain drive signal for the electronic control valve of the compressor which sets the swash plate position, and hence the compressor output/load. The suction pressure is typically not measured. The HVAC control only uses vehicle cabin temperature and evaporator air outlet temperature as control values. The construction is mostly stable but due to the suction pressure not being measured, there is no feedback that the actual suction pressure is achieved. The system is hence prone to static errors and hysteresis effects due to friction.

SUMMARY

A compressor control module (CCM) controls an output of a variable displacement swash plate compressor. The CCM directly calculates, or receives from an external source, a signal indicating a desired or required output from the compressor, receives a current value of the desired or required output, and receives or calculates a current rotation speed and angle, with respect to a rotation axis, of a swash plate, or a current piston stroke length and a reciprocating frequency of the compressor. The CCM determines a difference between the desired or required output from the compressor and the current value and outputs a signal to a valve driving unit which will adjust an angle of a swash plate such that the actual value becomes closer to, or the same as, the desired or required output, taking into account the additional values received or calculated in the receives or calculates step.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example with reference to the accompanying Figure, of which:

FIG. 1 is a sectional side view of a variable displacement swash plate compressor according to an embodiment;

FIG. 2 is a graph showing changes in opening level of a first communication passage and a second communication passage of the compressor depending on movement of a valve body;

FIG. 3 is a block diagram of a closed loop control according to an embodiment;

FIG. 4 is a graph of changes of suction pressure and opening level of valves in a process of increasing the inclination angle of a swash plate in the compressor;

FIG. 5 is a graph of changes of suction pressure and opening levels of valves in a process of decreasing the inclination angle of the swash plate;

FIG. 6 is a flow chart of a method for using a compressor control module to control an output of the compressor;

FIG. 7 is a block diagram of a control according to an embodiment;

FIG. 8 is a block diagram of a control according to another embodiment;

FIG. 9 is a block diagram of a control according to another embodiment; and

FIG. 10 is a block diagram of a control according to another embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Exemplary embodiments of the present invention will be described hereinafter in detail with reference to the attached drawings, wherein like reference numerals refer to like elements. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. According to the description of the various aspects and embodiments, elements shown in the drawings can be omitted if the technical effects of those elements are not needed for a particular application, and vice versa: i.e. elements that are not shown or described with reference to the figures but are described above can be added if the technical effect of those particular elements is advantageous in a specific application.

A variable displacement swash plate compressor according to an embodiment is shown in FIG. 1. The variable displacement swash plate compressor includes a center bore 11, which is formed through the center of a cylinder housing 10, and a plurality of cylinder bores 13, which are formed through a cylinder around the center bore 11. Pistons 15 may be movably disposed in the cylinder bores 13 and compress a working fluid in the cylinder bores 13.

A front housing 20, as shown in FIG. 1, may be coupled to an end of the cylinder housing 10. The front housing 20 may form a crank chamber 21 therein together with the cylinder housing 10. A suction chamber 31 that selectively communicates with the cylinder bores 13 may be formed in a rear housing 30. The suction chamber 31 may transmit a working fluid to be compressed into the cylinder bores 13.

As shown in FIG. 1, a discharge chamber 33 may be formed in the rear housing 30. A 4-way control valve 100 may be disposed at a side of the rear housing 30. The control valve 100 adjusts the angle of a swash plate 48 by alternatively adjusting the opening levels of a flow path (P1) between the crank chamber 21 and the suction chamber 31 and a flow path (P2) between the discharge chamber 33 and the crank chamber 21.

The control valve 100 selectively opens and closes the first communication passage P1 and the second communication passage P2, so that the bleed port can be closed, or substantially closed. By allowing pressure to be regulated in both directions, the bleed port can be reduced or closed, substantially improving efficiency. However, closing the bleed port makes the system less stable and small variation of control valve opening may lead to large change in swash plate angle. Closing or substantially closing the bleed port improves efficiency but makes the system complex to control. This invention describes a solution how to precisely control a compressor where the bleed port is closed or substantially reduced.

The variable displacement swash plate compressor might not comprise a bleed port or bleed valve between any of the suction chambers and crank chamber, or at least comprises a bleed port or bleed valve with reduced diameter. By removing the bleed port or bleed valve or reducing its diameter, the efficiency of the compressor is increased due to reduction of inner pressure loss and hence fuel can be saved.

A rotary shaft 40 may be rotatably disposed through the center bore 11 of the cylinder housing 10 and a shaft hole 23 of the front housing 20, as shown in FIG. 1. The rotary shaft 40 may be rotated by power from an engine (not shown). The rotary shaft 40 may be rotatably disposed in the cylinder housing 10 and the front housing 20 by a bearing 42.

A rotor 44 having the rotary shaft 40 passing through the center thereof to integrally rotate with the rotary shaft 40 is disposed in the crank chamber 21. The rotor 44 is formed substantially in a disc shape and fixed on the rotary shaft 40 and a protrusive hinge arm may be formed on a side the rotor 44.

The swash plate 48, in the embodiment shown in FIG. 1, may be hinged to the rotor 44 on the rotary shaft 40 to be rotated together. The swash plate 48 may be disposed such that the angle is variable with respect to the rotary shaft 40 in accordance with a discharge capacity of the compressor. That is, the swash plate 48 may be moved between a position perpendicular to the axis of the rotary shaft 40 and a position inclined at a predetermined angle from the rotary shaft 40. The swash plate 48 may be connected at the edge to the pistons 15 through a shoe. That is, the edge of the swash plate 48 is connected to connecting portions 17 of the pistons 15 through a shoe so that the pistons 15 are reciprocated in the cylinder bores 13 by rotation of the swash plate 48. A half-tilting spring providing elasticity may be disposed between the rotor 44 and the swash plate 48. The half-tilting spring may be disposed around the outer side of the rotary shaft 40 and provides elasticity such that the inclination angle of the swash plate 48 decreases.

In FIG. 1, a path connecting the crank chamber 21 and the suction chamber 31 is defined as a first communication passage P1 and a path connecting to the discharge chamber 33 and the crank chamber 21 is defined as a second communication passage P2. The passages are indicated by arrows in FIG. 1, and a working fluid flows in the directions indicated by the arrows due to a pressure difference among the suction chamber 31, crank chamber 21, and discharge chamber 33.

When the first communication passage P1 is opened, the crank chamber 21 and the suction chamber 31 communicate with each other, so the pressure in the crank chamber 21 decreases. Accordingly, the inclination angle of the swash plate 48 is increased, and consequently, the strokes of the pistons 15 are increased. Further, when the second communication passage P2 is opened, the crank chamber 21 and the discharge chamber 33 communicate with each other, so the pressure in the crank chamber 21 is increased. Accordingly, the inclination angle of the swash plate 48 is decreased and the strokes of the pistons 15 are decreased.

FIG. 2 is a graph with the transverse x-axis shows the movement distance of a valve body of the 4-way control valve 100 and the longitudinal y-axis shows the opening levels of the first communication passage P1 and second communication passage P2. It is shown in the left area that as the valve body is moved down, the second communication passage P2 is gradually closed until it is completely closed. It is shown in the right area that as the valve body is moved down, the first communication passage P1 is gradually opened. A section in which opening and closing of the first and second communication passages P1, P2 are reversed appears in an area around the origin, and it should be noted that there is no section in which the two communication passages P1, P2 are both open because this would lead to substantial leak of refrigeration fluid via the crank chamber 21. To facilitate control, it may also be possible to not completely close the bleed-port. This will result in both passages P1, P2 a little bit opened at the same time, which increases controllability.

In the embodiment, the control valve 100 does not use the entire section shown in FIG. 2, but is operated in the area indicated as a ‘control section’. Depending on leak from discharge chamber 33 to crank chamber 21 over the pistons 15, most of the control section is positioned at the section in which the opening/closing of the first communication passage P1 is adjusted. This is in contrast to the prior art, where control is done by opening a channel between the discharge chamber 33 and the crank chamber 21.

The control of the control valve 100 may be targeted at achieving a certain suction chamber pressure requested by a Heating Ventilation and Air Conditioning (HVAC) system. In order to improve the precision of achieved suction pressure with the bleed port closed, a pressure sensor may be included on an evaporator side of the refrigeration cycle, for example, in the suction chamber 31 of the compressor. The sensor measures the suction pressure. A control unit including a controller (such as a PI/PID controller) may further be included and configured to adjust the control valve 100 so as to close the gap between target and actual suction pressure. Feedback from suction pressure in closed loop increases stability and accuracy of the suction pressure control. However, the rather long delay in the refrigeration cycle may lead to controllability issues and make the control complex.

The HVAC system, for example of a vehicle, is shown in FIG. 3. A passenger cooling demand may be received by an HVAC Control Module. The HVAC Control Module, in turn, provides a target value to a compressor control module (CCM), which controls the control valve 100 of the compressor. Sensor values are fed back to the CCM to improve the control of the compressor. The compressor may affect the pressure in the evaporator and the evaporator air outlet temperature, which may be measured and provided to the HVAC Control Module. The feedback from measurements of the swash plate angle may be faster than feedback from suction pressure sensors. Typically, the feedback from swash plate angle may be significantly faster than feedback from sensors of suction pressure in response to compressor load changes. The use of sensors to provide information used to calculate current swash plate 48 position and/or compressor mass flow address problems related to the delay of the refrigeration cycle. In addition, by measuring swash plate angle, problems introduced by hysteresis, such as due to swash plate friction are significantly reduced. This leads to faster and more accurate control of the compressor.

For the calculation of the target value, other external signals may be taken into account, like outside air conditions (such as temperature and humidity), sun load on the vehicle, and target and actual value of the evaporator air outlet temperature.

FIG. 4 is a graph showing a regulation of suction pressure and changes of opening levels of valves in response to increased cooling demand according to one embodiment of the invention. An increased cooling effect is needed due to selection by a user, or other reasons. The CCM (and/or HVAC system) determines a suction pressure at which the corresponding cooling effect is achieved and sets the target suction pressure accordingly. The target suction pressure is input to the control unit. The suction pressure set value is shown by a dotted line in FIG. 4.

The control unit then applies control input to the electrical control valve 100 by applying a current to the electromagnetic actuator, so the opening level of the first communication passage P1 is increased. When the first communication passage P1 is increased, the crank chamber 21 and the suction chamber 31 communicate with each other, so the pressure in the crank chamber 21 decreases. The inclination angle of the swash plate 48 is increased, and consequently, the strokes of the pistons 15 are increased. This increases the load of the compressor (assuming constant rotation speed of the swash plate 48) and leads to pressure decrease in the evaporation side of the refrigeration cycle. Measured suction pressure is decreased and using a control algorithm of the controller, the control unit is configured to adjust the input to the control valve so that the target suction pressure is kept.

FIG. 5 is a graph showing a change of suction pressure and changes of opening levels of valves in a process of decreasing the strokes of the pistons 15 according to one embodiment of the invention. Needed cooling is decreased, due to selection by a user or other reasons. In order to decrease cooling the stroke length of the pistons 15 may be decreased, as described above. To this end, the control unit (such as the AC ECU) determines suction pressure at which the corresponding stroke can be obtained and sets the suction pressure as a target suction pressure. The suction pressure set value is shown by a dotted line in FIG. 5. When the target suction pressure value is changed into a higher value (i.e. lower cooling), the current applied to the electromagnetic actuator is decreased or blocked in accordance with an instruction from the control unit, and accordingly, the first communication passage P1 is closed and the second communication passage P2 is opened. When the second communication passage P2 is opened, the crank chamber 21 and the discharge chamber 33 communicate with each other, so the pressure in the crank chamber 21 is increased. Accordingly, the inclination angle of the swash plate 48 is decreased and the strokes of the pistons 15 are decreased. The output of the compressor is decreased leading to decreased evaporator temperature.

The above relates to a solenoid actuator. The skilled person would easily adjust the invention for using a stepped actuator, or any other suitable actuator.

If P2 channel is open long enough, the pressure in the crank chamber 21 becomes the same as the discharge pressure, so the inclination angle of the swash plate 48 is decreased to its minimum value. Without the compressor keeping the suction pressure low, the pressure in the evaporator will increase due to heating and additional refrigerant entering via the thermal expansion valve. When the suction pressure reaches the target value a current will again be applied to the actuator in order increase the stroke lengths to maintain an appropriate suction pressure.

As shown in FIGS. 4 and 5, a constant level of P1 opening level may be needed at stationary suction pressure to compensate for leak inside the cylinder into the crank room.

Example sensors providing information that can be used to calculate current compressor mass flow rate, include sensors providing information on swash plate rotation speed and angle. Another example of sensors providing information that can be used to calculate current swash plate angle and/or compressor mass flow rate, includes sensors providing information on piston reciprocation frequency and stroke length. Current swash plate angle and/or compressor mass flow rate may be measured and/or calculated in other ways. The swash plate rotation speed may be the same as the piston reciprocation frequency. The swash plate angle may be derived from the piston stroke length from pre-set data on compressor construction including the swash plate and piston structure.

FIG. 6 shows a flow chart of a method that may be used by the CCM to control the output (such as current compressor work) of a variable displacement swash plate compressor by:

a) either directly calculate, or receive 610 from an external source, for example the HVAC control unit, a signal indicating the desired or required output from the variable displacement swash plate compressor, for example, but not limited to, a suction pressure, a piston stroke length, an evaporator outlet air temperature, a refrigerant mass flow and/or a work done on fluid; b) receive 620 the current/actual value of the value described in a) c) receive or calculate 630 the current rotation speed and angle, with respect to the rotation axis, of the swash plate 48, or the current piston stroke length and its reciprocating frequency, respectively, of the variable displacement swash plate compressor; d) optionally receive or calculate 640 additional current values of the compressor, the air conditioning system or from the vehicle, like the discharge pressure, the crank case pressure, the delta pressure between suction pressure and crank case pressure, the evaporator outlet air temperature, the engine speed, but not limited to, e) determine 650 the difference between the desired or required output from the variable displacement swash plate compressor and the current output of the variable displacement swash plate compressor; and f) output 660 a signal to the valve driving unit which will adjust the angle of the swash plate 48 such that the actual output of the variable displacement swash plate compressor becomes closer to, or the same as, the desired or required output as obtained in step a), also taking into account the additional values received or calculated in c) and d).

The present CCM may drive the control valve to adjust pressure ratio between Pc and Ps to regulate the swash plate angle and output of the compressor in a closed loop control which may include the use of input signals from additional sensors. The signal output from the CCM at step f) may affect the valve driving unit that drives the actuator that drives the valve body to open one of the communication passages. The first passage opens PcPs and increases the angle. The second opens PdPc to decrease the swash plate angle.

The variable displacement swash plate compressor might comprise at least one delta pressure sensor that measures the pressure difference between the crank case pressure and the suction pressure, wherein the CCM is (optionally) adapted to use this information for step d).

In one example, the CCM contains automated control algorithms including an inner loop that is regulating the control valve actuator in order to achieve a certain swash plate angle and/or compressor discharge rate as set by an outer control loop in a cascade manner. The inner loop may be closed by input from sensors providing measurements that may be used to determine the swash plate angle or current compressor discharge rate. The delay may be relatively small compared to the delay from a suction pressure sensor, such as a delay well below one second.

One embodiment of a regulation of suction pressure with an inner loop regulating the swash plate angle is shown in FIG. 7. An inner loop may include a proportional-integral-derivative (PID) controller regulating the stroke length of the pistons 15. The inner control loop feedback delay time is typically well below one second. An outer loop may include the refrigeration cycle and a PID controller regulating Ps from a target Ps set point from the HVAC control System. The inner loop may comprise a piston stroke length feedback. The outer loop may comprise a Ps sensor feedback from a pressure sensor in the suction side of the refrigeration cycle, for example in the suction chamber 31 of the compressor.

The delay in the outer loop is longer than in the inner loop shown in FIG. 7, depending on the A/C system. The piston stroke length feedback is significantly faster than using only suction pressure measurement feedback. Measuring piston stroke length may substantially improve stability and response time of the control system. Direct piston stroke length feedback also overcomes controllability difficulties introduced by friction to swash plate movement. An incorrect position of the swash plate 48 may be measured, and control valve levels adjusted accordingly until the correct swash plate angle is achieved.

In addition, the swash plate position can be monitored before and/or during operation and certain failure detected if the swash plate 48 is not responding as expected to change in control valve changes.

A CCM according to an embodiment may also comprise a piston reciprocating speed sensor. Measurement from the piston reciprocating speed sensor may provide information on the piston reciprocation frequency to the inner and/or outer controller in a feedforward manner in order to pre-empt changes in engine rpm, allowing the control valve to be adjusted so that the stroke length compensate for the increased piston reciprocation frequency in order to keep the work load placed on the fluid constant. If the engine speed is increased suddenly, the increased compressor speed will be feedforward for example to the inner loop, and the stroke length decreased, so that a spike in compressor output is prevented. The spike would otherwise lead to torque peaks and to unnecessary cooling, and a waste of energy. As an example, the piston reciprocation cycle frequency and the piston stroke length of pistons 15 might be calculated by signals received from at least one speed-stroke sensor, such as speed-stroke sensor descried in European patent application 19159899.4.

Without using information on the rotation speed of the swash plate 48, such as the feedforward swash plate rotation speed, changes of compressor speed are only recognized by the controller after the suction pressure has changed. In such case, if the speed of the compressor is increased due a change of the engine rpm, the cooling effect of the air-conditioning system will be too high until the suction pressure has settled around the higher, desired level/value, leading to passenger discomfort and wasted energy. By sensing and responding to changes in compressor rotation speed (such as by feedforward), the CCM may react on speed variations earlier. In one embodiment, the compressor RPM and/or its derivative is used as input for the feed forward function in order to adjust the target piston stroke length value, e.g. by adding or subtracting certain values. In one embodiment, the adjustment may also take place at a different location of the control circuit, e.g. at the controller output value.

Examples of piston positioning sensors and piston speed sensors include eddy current sensor, cylinder pressure sensor, hall sensor, magneto-resistive sensor, capacity based sensor, and inductive based sensor.

By using the piston stroke length information, which corresponds to the swash plate angle, in an inner control circuit of a cascaded controller, the piston stroke length can be controlled directly. This significantly improves the control quality. It is also possible to use a difference between crank chamber pressure and suction chamber pressure (Pc−Ps) value instead of the piston length information for the 2nd controlling loop.

FIG. 8 depicts control according to an embodiment of the invention. An additional sensor is included to measure crank chamber pressure Pc. The pressure difference between crank case pressure and suction pressure (Pc−Ps) is calculated and used as actual value for the 3rd controller according to FIG. 8. In order to change the swash plate 48 angle, the pressure difference between Pc and Ps (Pc−Ps) needs to be below or above certain thresholds. Lower Pc−Ps pressure values increase the swash plate angle, higher Pc−Ps pressure values decrease the swash plate angle. If Pc−Ps is between the upper and lower threshold, the swash plate angle does not move at all due to static friction. Using Pc−Ps further improves control behavior in terms of response time and control quality as Pc−Ps is directly responsible for swashplate movement.

The input to the 1st controller in FIG. 8 is a difference between the suction chamber target pressure value and the measured suction chamber pressure value (in “barA”). The output signal of the 1st controller indicates a target piston stroke length that is compared with the measured value. The difference hereof is used as input to the 2nd controller (in “mm”). The difference is used by the 2nd controller to output a target pressure delta between crank chamber and suction chamber (Pc−Ps).

The output signal of the 2nd controller shown in FIG. 8 is compared with the measured Pc−Ps value and the difference is used as input to the 3rd controller that regulate the electrical control valve to reach this value. The output value of the 2nd controller, which is a Pc−Ps value, has no upper or lower limits and depends on the control deviation (input) of the 2nd controller and its control parameters.

FIG. 9 depicts control according to an embodiment of the invention. As the Pc−Ps thresholds for increasing and decreasing swash plate angle depend on different parameters (RPM, stroke, friction, temperature, etc.), knowledge about the accurate threshold values is an advantage. For example, in a certain condition the controller regulates the compressor to decrease the swash plate angle (by opening the PdPc passage, while the PsPc passage remains in a closed state). If there is a quite high Pd or if the PID parameters in this case have a rather large gain, the amount of control gas through the PdPc passage might be rather huge, resulting in a high Pc pressure increase and hence the Pc−Ps pressure also increases rapidly and the current Pc−Ps threshold, which might not suit the operational condition in this case, would be well overshot. The SWP angle decreases too rapidly as a result the controller needs to correct the SWP angle. In certain situations, this behavior might lead to oscillations of the swash plate angle. This problem is overcome by exactly determining the Pc−Ps thresholds during operation (online/in real time). By measuring the piston stroke length (which relates to SWP angle) and the Pc and Ps pressure, it is possible to determine the actual Pc−Ps thresholds at the current operational state.

At the time when the SWP angle changes, meaning its derivative is different from zero, or different from a certain tolerance band around zero, the corresponding Pc−Ps value is logically either the current lower Pc−Ps threshold or the current upper Pc−Ps threshold, and is stored in a “lower threshold variable” or a “upper threshold variable”. This can be done permanently, meaning that the Pc−Ps threshold values are updated constantly. The “2nd controller” uses these thresholds for precisely controlling SWP angle movement.

The feed forward function may also be used in relation to FIG. 7, FIG. 8, and FIG. 9 to further improve the dynamic behavior. An additional Ps information might be used to prevent icing of the evaporator. In certain embodiments, depending on certain system variables (such as Ps, piston stroke length, RPM, Pd, evaporator air outlet temperature, humidity, etc.) it might be advantageous to adjust the controller parameters of one or more of the controllers during operation. For example, depending on the current Ps and/or Pd and/or piston stroke length and/or opening level of the control valve, the PID parameters (proportional, integrative and differential parameters) may be adjusted. If Ps is lower, the P-parameter and/or I-parameter and/or D-parameter can be different compared to situations in which the Ps pressure is high, because for higher Ps, less control gas is sucked out of the crank room. If Pd is higher, the P-parameter and/or I-parameter and/or D-parameter can be lower compared to situations in which the Pd pressure is lower, because for higher Pd, more control gas is fed to the crank room. The variable displacement swash plate compressor might comprise at least one crank room pressure sensor wherein the CCM is (optionally) adapted to use this information for step d).

If the piston stroke length is low, the P-parameter and/or I-parameter and/or D-parameter can be higher compared to higher stroke situations. Depending on the control deviation of the outer control loop, it might be advantageous to adjust the I-parameter in order to increase the response of the controller. For example, if the control deviation is larger than a pre-defined limit, the I-Parameter can be set to larger values than for smaller control deviations.

Further, in order to improve controllability, for any embodiment described herein, a feed-forward function can be advantageous. This is because fast RPM changes cause the Ps to either increase or decrease. Without using these RPM changes as input value for the controller, the controller response to such RPM changes is very slow, because the suction pressure response is very slow (system related). In this case, the Ps pressure logically varies, which cause increases energy consumption because of unintended ramping of the Ps level/mass flow.

The compressor RPM value is used as input for the controller in order to improve the dynamic behavior in case of compressor RPM changes. For example, the compressor RPM and/or its derivative may be used as input for the feed forward function in order to adjust the input and/or the output of one and/or more than one controller loops.

Although exemplary embodiments were described above, the scope of the present disclosure is not limited to the specific embodiments and the present disclosure may be appropriately changed within the scope described in claims. For example, the suction pressure sensor may be disposed at one of the suction chamber 31 of the compressor, the outlet end of the evaporator, and a working fluid pipe between the evaporator and the compressor.

Although cascade control, PI, PID are mentioned in examples, any other type or construction of control mechanism may be used by the skilled person as the case may be, such as Model Predictive Control (MPC), Internal Model Controller (IMC), online predictive controller like neural network, Multi-Input-Single-Output (MISO) controller.

A thermostatic expansion valve (TXV) may control evaporator superheat temperature by adjusting mass flow. The compressor controls suction pressure that may be strongly linked to the evaporator temperature.

The control algorithm of the CCM may be located on a PCBA including a microcontroller, a valve driving unit, power supply, input units to read sensors and communication units to deliver and/or receive information to/from AC ECU and/or Engine ECU.

FIG. 10 depicts control according to an embodiment of the invention. The HVAC control unit provides a piston stroke length as target value for the CCM. A single controller is sufficient in this case to control the piston stroke length. 

What is claimed is:
 1. A compressor control module adapted to control an output of a variable displacement swash plate compressor, wherein the compressor control module: directly calculates, or receives from an external source, a signal indicating a desired or required output from the variable displacement swash plate compressor; receives a current value of the desired or required output; receives or calculates a current rotation speed and angle, with respect to a rotation axis, of a swash plate, or a current piston stroke length and a reciprocating frequency of the variable displacement swash plate compressor; determines a difference between the desired or required output from the variable displacement swash plate compressor and the current value; and outputs a signal to a valve driving unit which will adjust an angle of a swash plate such that the actual value becomes closer to, or the same as, the desired or required output, taking into account the additional values received or calculated in the receives or calculates step.
 2. The compressor control module of claim 1, wherein the external source is a heating ventilation and air conditioning control unit.
 3. The compressor control module of claim 1, wherein the desired or required output from the variable displacement swash plate compressor is a suction pressure, a piston stroke length, an evaporator outlet air temperature, a refrigerant mass flow and/or a work done on a fluid.
 4. The compressor control module of claim 1, wherein the compressor control module receives or calculates additional current values of the variable displacement swash plate compressor, an air conditioning system, or from a vehicle, such as a discharge pressure, a crank case pressure, a delta pressure between a suction pressure and a crank case pressure, an evaporator outlet air temperature, and/or an engine speed.
 5. The compressor control module of claim 1, wherein the steps are repeated in the claimed sequence until the current value is closer to, or the same as, the desired or required output.
 6. The compressor control module of claim 1, wherein the desired or required output is manipulated based on the additional values received or calculated in the receives or calculates step.
 7. The compressor control module of claim 1, wherein an upper and/or a lower threshold difference between a crank chamber pressure and a suction pressure difference, exceeding the upper threshold results in an swash plate angle increase and undershooting the lower threshold results in a swash plate angle decrease, is stored while a derivative of piston stroke length is different from zero or different from a certain tolerance band around zero, the upper and/or lower threshold difference or a function of the upper and/or lower threshold difference is used for swash plate angle control.
 8. The compressor control module of claim 1, wherein a compressor rotation speed and/or derivatives of the compressor rotation speed are fed forward to the compressor control module in order to adjust an input and/or an output of one and/or more than one controller loops to improve dynamic behavior in case of changes in compressor rotations per minute.
 9. The compressor control module of claim 1, wherein the signal to the valve driving unit is at least in part generated from an output of a Model Predictive Control, an Internal Model Controller, an online predictive controller like neural network, and/or a Multi-Input-Single-Output controller.
 10. The compressor control module of claim 1, wherein the signal to the valve driving unit is at least in part generated from an output of a PID controller, the determined difference is an input signal to the PID controller.
 11. The compressor control module of claim 10, wherein at least one gain parameter of the PID controller is at least in part adjusted based on one or more measured or calculated values of the compressor, the measured or calculated values are at least one of: a suction chamber pressure, a discharge chamber pressure, a piston stroke length, a piston reciprocating frequency, and opening level of a control valve.
 12. The compressor control module of claim 11, wherein, when the suction chamber pressure is low, a P-parameter and/or an I-parameter and/or a D-parameter is lower compared to when the suction chamber pressure is higher; and/or when the discharge chamber pressure is high, the P-parameter and/or the I-parameter and/or the D-parameter is lower compared to when discharge chamber pressure is lower; and/or when the piston stroke length is low, the P-parameter and/or the I-parameter and/or the D-parameter is higher compared to when the piston stroke length is higher.
 13. A variable displacement swash plate compressor, comprising: a compressor control module adapted to control an output of the variable displacement swash plate compressor, the compressor control module: directly calculates, or receives from an external source, a signal indicating a desired or required output from the variable displacement swash plate compressor; receives a current value of the desired or required output; receives or calculates a current rotation speed and angle, with respect to a rotation axis, of a swash plate, or a current piston stroke length and a reciprocating frequency of the variable displacement swash plate compressor; determines a difference between the desired or required output from the variable displacement swash plate compressor and the current value; and outputs a signal to a valve driving unit which will adjust an angle of a swash plate such that the actual value becomes closer to, or the same as, the desired or required output, taking into account the additional values received or calculated in the receives or calculates step.
 14. The variable displacement swash plate compressor of claim 13, wherein the variable displacement swash plate compressor does not have a bleed port or a bleed valve between a suction chamber and a crank chamber or has a bleed port with a reduced diameter.
 15. The variable displacement swash plate compressor of claim 13, further comprising at least one speed-stroke sensor, the speed-stroke sensor monitors a piston stroke length and a reciprocating speed of one, or more, of a plurality of pistons of the variable displacement swash plate compressor and sends the measurement to the compressor control module.
 16. The variable displacement swash plate compressor of claim 15, wherein the compressor control module, on the basis of an amount of travel of the one of more pistons, calculates the angle of the swash plate and/or the piston stroke length of the variable displacement swash plate compressor and, on the basis of the reciprocating speed of the piston, calculates the swash plate and the compressor rotational speed.
 17. The variable displacement swash plate compressor of claim 13, further comprising an electronic control valve connected to the compressor control module and adapted, in response to receiving the output signal at the valve driving unit, to direct pressure from a crank chamber to one or more of a plurality of suction chambers or from a discharge chamber to the crank chamber, changing an angle of the swash plate.
 18. An air conditioning system, comprising: a variable displacement swash plate compressor including a compressor control module adapted to control an output of the variable displacement swash plate compressor, the compressor control module: directly calculates, or receives from an external source, a signal indicating a desired or required output from the variable displacement swash plate compressor; receives a current value of the desired or required output; receives or calculates a current rotation speed and angle, with respect to a rotation axis, of a swash plate, or a current piston stroke length and a reciprocating frequency of the variable displacement swash plate compressor; determines a difference between the desired or required output from the variable displacement swash plate compressor and the current value; and outputs a signal to a valve driving unit which will adjust an angle of a swash plate such that the actual value becomes closer to, or the same as, the desired or required output, taking into account the additional values received or calculated in the receives or calculates step.
 19. The air conditioning system of claim 18, wherein the air conditioning system is in an automobile and the compressor control module ensures that a temperature in a cabin of the automobile is maintained at a desired, or set, temperature by users of the automobile by controlling a suction pressure or an output of coolant of the variable displacement swash plate compressor.
 20. The air conditioning system of claim 19, wherein the desired output of the variable displacement swash plate compressor is an amount of work done on the coolant, and which remains constant irrespective of a driving force and rotation speed of the variable displacement swash plate compressor. 